66 PERSPIRATION. 



Thus, in curvilinear iron hot-houses, in which 

 the atmosphere becomes so dry in consequence 

 of the heat that plants perish, it is necessary 

 that the air should be rendered extremely hu- 

 mid, by throwing water upon pavement, or by 

 introducing steam. 



And in transplantation in dry weather, ever- 

 greens, or plants in leaf, often die, because tiie 

 spongioles are destroyed, or so far injured in 

 the operation as to be unable to act, while the 

 leaves never cease to perspire. 



The greater certainty of transplanting plants 

 that have been growing in pots is from this lat- 

 ter circumstance intelligible ; 



While the utility of putting cuttings or newly 

 transplanted seedlings into a shady damp at- 

 mosphere, is explained by the necessity of les- 

 sening evaporation produced by solar light. 



The admission of air or ventilation, as it is 

 called, is not generally well understood by gar- 

 deners. Much light has been thrown on this 

 subject, since the invention of the air tight 

 boxes of Mr. Ward, in which, owing to the 

 total exclusion of currents of air (ventilation) 

 the evaporation from the surface of the earth 

 and plants is constant, according to the heat, 



